Carrier frequency amplifier



April W43. H. HANNEMANN ETA 2,317,764

CARRIER FREQUENCY AMPLIFIER Filed Dec. 13, 1940 Patented Apr. 27, 1943 UNITED STATE I PATE CARRIERFREQUENCY AMPLIFIER g Heinz Hannemann and Ewald Oberltirider, Ber

lin, Germany; todian Application December 13 In Germany De vested in'the Alien Property Cus- 1940, SerialNo. 370,048 cember 12, 1939 Claims. (01. 179 171) In carrier frequency telephone systems it is in several respects importantto control the amplification effected by'carrier frequency repeaters. In many cases an automatic control is desirable in order to stabilize the telephonic connections.

In the case of uni-directional transmission systems, such as wired radio broadcasting systems, a constant transmission level is particularly desirable on account of the modulation and especially with a view to avoiding over-modulation of the subsequent repeaters and transmitters. The transmission level considerably varies where open 4 lines are employed and in this case depends on weather and season conditions. With cables the level undergoes variations which are mainly due to season conditions and are comparatively small,

ling the transmission level act to rectify the guide frequency or the carrier frequency, as the case may be, by means of an additional device and they utilize the variable intensity of the resultant current for indicating a level increase or decrease with the aid of maximum or minimum relays, respectively, so-called marginal relays which are similar in structure to contact ammeters and voltmeters. This method, however, is insufficient inasmuch as these relays, having to respond or to release at predetermined current intensities, are sensitively adjusted and yet not reliable in operation. Besides they are sensitive to mechanical disturbances, such as shocks.

The present invention has for its object to provide means whereby an. increase or decrease of the transmission level is indicated'by\the rectified current having positive direction in the event of a'level increase and negative direction in the event of a level decrease, or vice versa. No continuous current is effective whenever the level agrees with the desired value. This principle also entails that the continuous current, caused by the level not agreeing with that value, even with small level variations becomes intense enough to insure a safe response of the respective signalling relay.

Accordingto the invention this object issecured with the aid of a direct current bridgeconnection that comprises four resistances, orient-these 'resistances or a number thereof being capable of varying under the influence of the carrier frequency..

In thedrawing, Fig. 1 is a diagram illustrating the fundamentalidea of the invention. Fig. 2'is 'a diagram showingone embodiment of the invention, this embodiment beingbased on the arrangement represented in Fig.1. Fig. 3 is a graph referred to in explaining the operation of the systemillustrated in Fig. 2. Fig. 4 is a diagram that shows a modification of the device'represented' in Fig. 2. g

The. bridge connection shown inFig. 1 com.- prises four resistances R1, R2, R3, Rx and indicating devices which constitute the middle of the bridge and comprise direct current relays V, W'

arranged to-respond to currents of definite direction, the direction in the case of each relay being I opposite to that of the other relay. Resistance Rx is arranged to vary under the influence of the carrier frequency and in its resistivity depends upon the amplitudes. This resistance may be constituted by a vacuum tube D, Fig. 2, whose working point is so adjusted that the internal resistance of such tube shall balance the bridge, whenever the measured level agrees with the desired level. In addition, variable resistances having an ascending or a descending resistance characteristic may be included in the bridge,

namely, resistances which under the influence of the variation of R1: act to vary their own resistance under the influence of'the variation of Rx.

With the vacuum tube D employed as resistance Rx the working point of this tube is displaced by the carrier frequency rectified by the tube. The displacement is such that the internal resistance of the tube is decreased if, for instance, the level rises beyond the desired level, whereas it is increased whenever the level becomes less than the desired value, or vice versa. This behaviour means that with-a change of the internal resist-v ance RX of the tube the bridge'balance is afl'ected in such a manner that on increase of resistance RX a bridge current flows from B to A, Fig. 1, while'decrease of resistance Rx causes a bridge current to flow from A to B. Consequently, relay Wresponds on resistance Rx increasing over the desired value, while relay V responds on the resistance Rx decreasing.

In order further to increasethe variation of the internal resistance as regards the action on the relays V, W the arriving carrier amplitude is {rectified in an additional .change the grid bias of the tube in increase the action on described arrangement; .is alteredtofaid the grid potential.

The interrelation between the control direct current and the oncoming carrier amplitude is in Fig. 3 illustrated as test reading. a A further feature of the invention is thatthe arranged in advance of the control repeater but is included therein, being disposed in the anticoupling path, for instance.

Fig. 4 illustrates an anti-coupling for the tube D, which by way of example to a resistance Ra and a condenser Ca in order to causethe internal resistance to vary uniformly within the available working'range of the tube whenever the working point is displaced in accordance with a higher or lower potential.

What is claimed is:" r

1. Automatic level control means for carrier frequency amplifiers, comprising a direct current bridge connection including four resistances at least one thereof being variable when affected by carrier frequency, means affected by carrier frequency to alterthe variation of said one resistance, and direction-responsive direct current relays connecting the center points of said bridge.

' 2. Automatic level control means for carrier frequency amplifiers, comp sing a direct current bridge connection includingfour-resistances, a

vacuum tube constituting one of said resistances whereby said one resistance is variable when is shown to be joined affected by carrier frequency, means affected by of said bridge.

carrier frequency to alter the variation of resistance of said tube and direction-responsive direct current relays connecting the center points 3. Automatic level control means for carrier frequency amplifiers, comprising a direct current means for regulating the amplification is not connection including, a

,. having a grid, means to bias said lays connecting whenever the working point bridge connection including a plurality of resistances, a vacuum tube constituting one of said resistances whereby said one resistance is variable when affected bysaid carrier frequency, said tube grid, a rectifier to alter the carrier voltage in the anode circuit of said tube to-alter the bias of said grid, and direction-responsive. direct current relays connecting the center points of said bridge.

4. Automatic level control frequency amplifiers, comprising means, including a vacuum tube having a grid, torectify incoming carrier currents, a direct current bridge plurality of resistances one thereof being said vacuum tube, means to bias said grid, means to alter the bias of said grid and direction-responsive direct current rethe center points of said bridge. level; control means for carrier frequency amplifiers, comprising a direct current bridge connection including a plurality oi resistances, one thereof being a vacuum tube having a grid, means to bias said grid, rectifying means to 5. Automatic alter the bias of said grid, means to cause the internal resistance of the tube to vary uniformly within the available working range of the tube direction-responsive direct current relays connecting thecenter points of said bridge.

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means for carrier is displaced, and 

